How to Flash a T-Mobile to AT&T

If you currently use T-Mobile's wireless service but want to change to AT&T instead, you must prepare your phone to accept a SIM card from AT&T. Sometimes incorrectly referred to as "flashing," this process is more commonly called "unlocking." Flashing is the process of reprogramming a CDMA phone to work with a different CDMA network, such as switching from Verizon to Sprint. The CDMA network doesn't use SIM cards, but the GSM network does. Your phone was programmed to accept only T-Mobile SIM cards before you purchased it, so you must unlock it to use it with AT&T.

Don't be stuck with one provider -- unlock your phone to use it with other carriers.

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Step

Call AT&T to set up a new wireless account. Tell the customer service representative you plan to use your existing phone.

Step

Dial "*#06#" on your phone's keypad and write down the IMEI number that appears. It's also located under your battery in the battery compartment.

Step

Call T-Mobile customer service to request your phone's unlock code. You must have purchased the phone from T-Mobile and have been a customer for at least 40 days on a post-paid plan or 60 days on a pre-paid plan. If you don't qualify for T-Mobile's unlock code, visit a website that offers unlock codes for a fee, such as Unlock to Talk, GSM Liberty or Global Unlock.

Step

Provide T-Mobile or the online code retailer your IMEI number and phone model number. Both should ask for your email address and online retailers ask for payment information. T-Mobile provides codes for free to eligible customers, and the customer service representative may be able to give you the unlock code over the phone.

Step

Retrieve the unlock code from your email or write it down if T-Mobile provides it over the phone.

Step

Turn off your phone and then remove your battery and SIM card. Place the AT&T SIM card into the slot and then replace the battery and turn on the phone.